That is true. Apple's trade in values are not the best. But that doesn't mean you cannot trade an iPhone that was repaired by them , to them for a new one and paying the difference .
Of course, but that would be a very costly solution, presumably to go from an iPhone XS to XS Max.
The only reason I mentioned warranty is that the damaged iPhone would retain the original factory warranty (if repaired by Apple) and the OP's AppleCare would still be in effect for the balance of the term.
But if the OP wants to change the iPhone model, then the most cost effective approach would be to get the XS repaired, ask Apple for partial credit on the AppleCare term, then sell the XS on the open market. IIRC, Apple's trade-in program (aka "GiveBack") provides only about half the value of a phone in the first year. Not too bad if you've owned the phone for a year, but losing half the value in just a few short months, on top of paying $200 for a screen repair, that would really hurt!